In conventional cellular and PCS (personal communications system) wireless systems, signals transmitted from a base station (cell site) to a user (remoter terminal) are usually received via an omni-directional antenna; often in the form of a stub antenna. These systems often sacrifice bandwidth to obtain better area coverage, stemming from the result of less than desirable signal propagation characteristics. For instance, the bit (binary digit) to Hz ratio of the typical digital Cellular or PCS system is often less than 0.5. Lower binary signal modulation types, such as BPSK (Binary Phase Shift Keying) are used, since the effective SNR (Signal to Noise Ratio) or C/I (Carrier to Interference Ratio) are often as low as 20 dB. In fact, for voice based signaling, the threshold C/I (or S/N) ratio for adequate quality reception of the signal is about 17 dB.
For wireless systems directed towards data applications, it is desirable to significantly increase the SNR or C/I in order to employ higher order (binary) modulation techniques, such as QAM-64 (Quadrature Amplitude Modulation, with 64 points in the complex constellation). These higher order modulation schemes require substantially greater C/I (or SNR) thresholds; typically higher than 26 dB. For the case of MMDS (multi-user multipath distribution system) signals, where the carrier frequencies are higher (around 2500 MHz), the propagation characteristics are even worse. There is a need therefore for transmission systems that can both satisfy the coverage (propagation) demands,,as well as generate high C/I or SNR levels.
One option is to increase the size of the terminal equipment (TE), or remote, antenna gain. This requires increasing the size. Additionally, it helps to increase the elevation (i.e., vertical height above ground level) of the antenna. The higher you place an antenna, the better the system gain. For a simple planar earth model, the total system path loss (attenuation) is a function of each (transmit and receive) antenna""s directive gain (towards one another). However, this path loss is also a function of the height (from ground level) of each antenna. Thus, as you increase the height, from ground, the total system path loss decreases, which is an increase in the overall system link performance, or system gain. The link performance (system) gain increases 6 dB every time you double one of the antenna""s height from the ground level. If you double both (i.e., transmitting and receiving) antennas"" heights, the total gain (link performnance) goes up by 12 dB (6 dB+6 dB). Therefore, doubling the height from the ground is equivalent to quadrupling the size (area) of the antenna; which produces 4xc3x97 (or 6 dB) of directive gain.
In conventional analog MMDS systems, this (i. e., increase of SNR or C/I) has been traditionally accomplished by installing a large reflector type antenna (with up to 30 dBi of directional gain) on a rooftop, or a pole. The disadvantages are a complex, difficult, and costly installation; as well as poor aesthetics.
The migration of the MMDS frequency spectrum, from an analog video system, to a wireless data and Internet system, demands a more user friendly (easier) installation method, with much lower cost. The difficulty here is designing a system with sufficient directional gain, as to overcome loss with transmission through walls, as well as being easy to install, and orient; by the consumer, or other persons without specialized skills.
In accordance with one aspect of the invention, there is provided an easy to install, high gain, omni-directional xe2x80x9cindoorxe2x80x9d antenna which provides omni-directional coverage. No installation, xe2x80x9cpointingxe2x80x9d or orientation is required, and the antenna may be installed indoors in a corner of a room.
In accordance with another aspect of the invention, four antenna elements are formed as a xe2x80x9cbook,xe2x80x9d that is, two each, back to back; with the pairs oriented at 90xc2x0 to each other, such that each separate antenna covers a 90xc2x0 sector, so that the coverage of the antennas when summed creates a full 360xc2x0 coverage.
In accordance with another aspect of the invention, an indoor antenna comprises a unitary support structure having a plurality of support surfaces; at least one antenna element mounted to each of the support surfaces; and the support surfaces being
In accordance with another aspect of the invention, a method of transmitting and receiving RF signals comprises coupling a first support member having a first pair of opposed planar support surfaces along a common edge with a second support member having a second pair of opposed planar support surfaces, orienting the first and second support members such that first pair of planar support surfaces are substantially orthogonal to the second pair of planar support surfaces, mounting at least one antenna element to each of a plurality of support surfaces, and arranging the support surfaces in a unitary support structure with the support surfaces oriented to achieve substantially 360xc2x0 coverage by the antenna elements.
In accordance with another aspect of the invention, a method of transmitting and receiving RF signals comprises mounting at least one antenna element to each of a plurality of support surfaces, and arranging the support surfaces on a unitary support structure with the support surfaces and antennas oriented to achieve substantially 360xc2x0 coverage.